1. Field of the Invention
The present invention relates to a method of manufacturing a low temperature co-fired ceramic (LTCC) substrate, and more particularly, to a method of manufacturing a capacitor-embedded LTCC substrate, capable of being employed as a package substrate for modules of electronic products.
2. Description of the Related Art
Recently, a more compact and higher frequency trend of various electronic products has increased a call for smaller size, lighter weight and multi-functionality of the parts embedded therein. Meanwhile, electronic products are required to possess a high-power capacitor for decoupling to protect themselves from noises caused by division of electric power among each functional module. This increases the number of conventional surface-mounted capacitors, thereby increasing the size or height of a substrate or module.
FIG. 1 is a cross-sectional view illustrating a high frequency module structure employing a conventional LTCC substrate which has drawn attention due to low-loss high-frequency characteristics.
Referring to FIG. 1, a high frequency module 10 includes an LTCC substrate 11 formed of a plurality of LTCC layers 11a to 11e, and a passive device such as an IC chip 16 and a capacitor 15 mounted on the substrate 11. The LTCC layers 11a to 11e each are provided with a conductive pattern 12 and a conductive via hole 13 to serve as a desired circuit.
As described above, the capacitor 15 needs to be bigger-sized in line with the recent trend of products, thereby rendering it hard to reduce the size of the module itself.
To overcome this problem, studies have been vigorously conducted to develop a method of embedding a passive device such as a capacitor in a substrate such as a printed circuit board (PCB). However, in the LTCC substrate shown in FIG. 1, a high dielectric material for a high-power capacitor has a firing shrinkage rate considerably different from a low-temperature co-fired ceramic. This poses a practical difficulty to the manufacture of the capacitor-embedded LTCC substrate.
Of course, in some of surface mount device (SMD) components, sheets with a low dielectric constant and sheets with an intermediate dielectric constant of typically up to 100 are co-fired to manufacture small parts such as a bandpass filter and a balance filter. However, in a relatively big LTCC substrate used in the module, a heterogeneous dielectric material has been rarely adopted. As described above, studies have been carried out only on co-firing of the material with an intermediate dielectric constant and the material with a low dielectric constant.
As a result, a high-power capacitor having a capacitance of 100 pF to several nF has the SMD components surface-mounted thereon.